The present disclosure relates to exhaust gas-driven turbochargers for internal combustion engines.
The transient response of internal combustion engines in passenger vehicles and trucks is a critical parameter in terms of overall driveability and efficiency of the engine system. When the engine is boosted by an exhaust gas-driven turbocharger, it is often difficult to provide sufficient air to the engine at low engine speeds so as to rapidly accelerate the engine and vehicle. This is due in part to the low exhaust gas energy and hence low turbine power extraction at low engine speed.
One approach that has been proposed for alleviating this poor responsiveness at low engine speeds, specifically for medium- and heavy-duty trucks, is to use pressurized air from the air cylinders of the truck's air-assisted brake system (or from a separate pressure vessel charged by the air-assisted brake system) to supply air to the engine intake system at low engine speeds. Such proposals typically employ a three-way valve having two inlets and one outlet. One inlet is connected to the compressor and the other inlet is connected to the air cylinder. The valve can be operated to supply either the compressor discharge air or the pressurized air from the air cylinder through the valve outlet to the engine intake.
A drawback of this approach is that when the valve is positioned to shut off the compressor air flow to the engine, the compressor can become unstable and possibly go into a surge condition, which can create unwanted vibration and noise and/or can damage the turbocharger bearing system.